1. Field of the Invention
The present invention relates to a process for producing cyclohexyl acetate, and more particularly, to a process for producing cyclohexyl acetate by the reaction of acetic acid with cyclohexene in the presence of heteropolyacids mainly composed of oxides of tungsten.
2. Description of the Related Art
Heretofore, as processes for producing cyclohexyl acetate, there have been generally known an esterification method of acetic acid with cyclohexanol and a reaction of cyclohexanol with acetic anhydride.
However, both processes use cyclohexanol as a starting material, and cyclohexanol has a problem as to the method for preparation thereof and other various drawbacks. In addition, the esterification reaction is an equilibrium reaction so that it is difficult to produce the ester in high yield and moreover it is necessary for removing the water as a by-product in order for the reaction to proceed.
In the method of using acetic anhydride, although the yield of the ester is high, there are many various drawbacks, for example: acetic anhydride is expensive and in addition, one molecule of acetic acid is released and it is very difficult to convert the acetic acid into the anhydride.
For the purposes of solving these problems, some methods for producing cyclohexyl acetate by an addition reaction of cyclohexene with acetic acid have been recently proposed. For example, Japanese Patent Application Laid-open No. 254634/1989 discloses a method for producing cyclohexyl acetate by the reaction of cyclohexene with acetic acid in the presence of a strongly acidic cation exchange resin as a catalyst.
According to this method, the reaction should be effected at 130.degree. C. for 5 hours. However, in general, the heat resistant temperature of such strongly acidic cation exchange resins are inherently about 100.degree. C., and even highly heat resistant resins can not withstand a temperature higher than 160.degree. C. Therefore, when such ion exchange resins are used, a high reaction temperature and a long reaction time are required. In addition, these ion exchange resins have also drawbacks that the mechanical strength is low and the resins are easily broken so that the stability as a catalyst is unreliable to a great extent and further the catalytic activity is low.
Japanese Patent Application Laid-open No. 313447/1989 discloses an addition reaction of acetic acid with cyclohexene in the presence of both ZSM-5, a high silica content-zeolite, as a catalyst and water. According to this method, the reaction temperature is 120.degree. C. and the reaction time is 4 hours resulting in the formation of cyclohexanol in a 12.5% yield and cyclohexyl acetate at most in a 65% yield. The reaction temperature is high and the catalytic activity is low.
The present inventors have conduct research on efficient methods for the production of cyclohexyl acetate, and noted that the addition reaction of cyclohexene with acetic acid is an excellent method for producing cyclohexyl acetate and have considered the conventional drawbacks such as low catalytic activity, and low durability as catalyst including low mechanical strength and low heat resistance. As a result, the present invention has been completed.